Samples such as solid (bulk), liquid, wipe or an air filter are routinely analyzed for a variety of metallic contaminations. Solid samples such as dust and soil are collected and subjected to a dissolution solution to dissolve the metal or metal compound of interest. Liquid samples such as water may also be analyzed, but in this case dissolution process is not necessary. Wipes are used to determine surface contamination of articles and after wiping a specific amount of area these are subjected to dissolution. Similarly, the air-sampling device comprises of a filter through which a specific volume of air is passed and then the filter is analyzed to determine airborne pollution from the metal of interest after subjecting the filter to dissolution. Most of the quantitative test methods to analyze metals go through a dissolution process and then an analytical procedure to quantify the metal. Some examples of the analytical test methods where dissolution and then an analysis are carried out are NIOSH 7301 (NIOSH is National Institute of Occupational Health and Safety, Atlanta, Ga.), where the material is dissoluted using aqua regia, EPA procedure SW-846-3051 (EPA is US Environmental Protection Agency, Washington D.C.) uses microwave digestion with nitric acid. In all these test methods the samples are then analyzed using plasma methods, which typically are not affected by organic impurities. Organic impurities are usually colored, may bind to other molecules that result in color or fluoresce, or can have strong fluorescence signals. In either case all of these may interact with optical detection methods. For those methods that rely on fluorescence, this interference can be two fold, first it can absorb the excitation energy and thus lowering the excitation signal available for the intended fluorophore, and secondly if the impurities emit in the same wavelength region as the intended fluorophore then the analysis may falsely provide elevated levels of metal when only low concentrations of metal are present. Thus in test methods such as NIOSH 7704, 9110 and ASTM D7202 for beryllium analysis by fluorescence such interferences can be severe. Such interferences can also influence optical analytical methods for a variety of other metals, e.g., NIOSH 7703 and EPA SW846-7196 for hexavalent chromium, and NIOSH 7700 for lead. Thus it is desirable to reduce or eliminate interferences due to the organic impurities that will interfere with the results.
Although this invention is applicable to all types of optical analysis for metals, it will be mainly illustrated for analysis of beryllium by fluorescence. Beryllium is a metal that is used in a wide variety of industries including electronics, aerospace, defense, and the US Department of Energy (DOE) complexes. Exposure to beryllium containing particles can lead to a lung disease called Chronic Beryllium Disease (CBD). CBD involves an uncontrolled immune response in the lungs that can lead to deterioration in breathing capacity and ultimately death. It is clear that even in processes where beryllium dust has been controlled to very low levels, cases of disease still persist. In fact, there have been cases of CBD reported in people that have had no obvious direct contact with beryllium operations. Despite the fact that very low exposure levels can lead to CBD, the onset of disease can take decades. Thus it is important that any analytical method provide an accurate assessment of the beryllium or any other metal where this information is used further to make decisions. Optical fluorescence is used to determine beryllium in several standard test methods, e.g., NIOSH 7704, NIOSH 9110, ASTM D7202 and ASTM D7458. These methods follow steps where a sample comprising beryllium or its compound is dissoluted in an aqueous solution of ammonium bifluoride. An aliquot of this solution is added to a buffered solution of an indicator solution comprising 10-hydroxybenzo[h]quinoline-7-sulfonate (10-HBQS) dye. This solution is measured for fluorescence signal to quantify beryllium. An organic impurity in the sample that may have fluorescence characteristics similar to 10-HBQS can result in a significant error.
One object of the present invention is to demonstrate practical methods of removing the effects of organic impurities from analytes that are analyzed for metal content using optical methods.
Yet another objective of this invention is to demonstrate practical methods of removing the effect of the organic impurities from analytes that are analyzed for beryllium by fluorescence.